The physiological stress for the users of safety suits is very high because the temperature and humidity rise very rapidly in the suit during physical exertion. The high humidity of the air, in particular, has the consequence that the user cannot sufficiently release his or her body heat any longer, since the heat is released mainly by sweating during physical exertion. The mission of rescue teams using safety suits is very limited in time due to this circumstance and the mission time is therefore only 20 minutes to 30 minutes, maximum. Only little time and energy are left for the rescue mission proper and the return if long distances are to be covered to reach the mission site.
Humans are definitely capable of performing physical activity over several hours even at ambient temperatures of 42° C. if the humidity of the air is relatively low, i.e., below 30% relative humidity. Even though the body temperature does rise somewhat in the process, it will then remain at a stable level. This also applies to the heart rate.
The body temperature rises steadily and the test subject will become exhausted very rapidly at a markedly reduced air temperature of 32° C. but a very high relative humidity of 84%. The circumstance that exhaustion is accelerated in persons who use a safety suit by the fact that a respirator also must be carried by the person besides the safety suit is to be taken into consideration.
A safety suit, in which air is fed into the safety suit by means of a blower from the outside and is released from the safety suit via a pressure relief valve, is known from EP 1 494 760 B1. Even though a measurable cooling effect is obtained due to the rinsing with air, moisture cannot be prevented from becoming enriched in the interior space of the suit and from being condensed on the material of the safety suit. The condensate collects partially on the clothing, which is unpleasant for the user of the suit. In addition, the blower draws in ambient air, which may be contaminated and must be thoroughly filtered. The residual risk that contaminated air may enter the interior space of the safety suit is not accepted by the users.
Liquid cooling is also used to cool a person or to regulate the person's temperature. This is used in space suits, but also in chemical safety suits. However, this principle has limited effect because it acts directly on the skin on the basis of the conductive cooling effect. The skin temperature must be kept so cool that no sweating occurs and this leads as a result to nonphysiological or very unpleasant, cold skin temperatures. The cooling source proper is arranged, besides, outside the suit. The entire cooling energy must be carried along in case of a mobile device, which leads to heavy weights of about 12-18 kg additionally and to a correspondingly large overall volume. Water ice storage units carried along have corresponding net weights of 3.23 kg for the ice plus the own weight of the housing for a hypothetical cooling energy of 1,080 kJ, which corresponds to a cooling capacity of 800 W over 30 minutes. The handling of water ice is cumbersome because the ice must first be made and finally removed from the cooling containers and introduced into the cooling device. A safety suit with a cooling source appears, for example, from DE 28 46 139 C2.
A safety suit, in which the air of the interior space is circulated by means of a blower and both carbon dioxide and moisture are removed in the process, is known from U.S. Pat. No. 3,174,300. The oxygen consumed is replaced. A chamber filled with a coolant is used to separate moisture, and the condensate formed is collected in a collection tank. A coolant must be carried along and replaced after a certain use time. The cooling energy available is greatly limited due to the weight of the coolant carried along.